bpf: prevent leak of lsm program after failed attach

In [0], we added the ability to bpf_prog_attach LSM programs to cgroups,
but in our validation to make sure the prog is meant to be attached to
BPF_LSM_CGROUP, we return too early if the check fails. This results in
lack of decrementing prog's refcnt (through bpf_prog_put)
leaving the LSM program alive past the point of the expected lifecycle.
This fix allows for the decrement to take place.

[0] https://lore.kernel.org/all/20220628174314.1216643-4-sdf@google.com/

Fixes: 69fd337a975c ("bpf: per-cgroup lsm flavor")
Signed-off-by: Milan Landaverde <milan@mdaverde.com>
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Stanislav Fomichev <sdf@google.com>
Link: https://lore.kernel.org/r/20221213175714.31963-1-milan@mdaverde.com

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 35972afb685049ebebe6ed1435dab14e066a6058..64131f88c5537076a25bcfb13a04d81ea9a19ce4 100644 (file)
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -3518,9 +3518,9 @@ static int bpf_prog_attach(const union bpf_attr *attr)
        case BPF_PROG_TYPE_LSM:
                if (ptype == BPF_PROG_TYPE_LSM &&
                    prog->expected_attach_type != BPF_LSM_CGROUP)
-                       return -EINVAL;
-
-               ret = cgroup_bpf_prog_attach(attr, ptype, prog);
+                       ret = -EINVAL;
+               else
+                       ret = cgroup_bpf_prog_attach(attr, ptype, prog);
                break;
        default:
                ret = -EINVAL;